October 26, 2010: The globular star cluster Omega Centauri has caught the
attention of sky watchers ever since the ancient
astronomer Ptolemy first catalogued it 2,000 years ago.
Ptolemy, however, thought Omega Centauri was a single
star. He didn't know that the "star" was actually a
beehive swarm of nearly 10 million stars, all orbiting
a common center of gravity. The stars are so tightly
crammed together that astronomers had to wait for the
powerful vision of NASA's Hubble Space Telescope to
peer deep into the core of the "beehive" and resolve
individual stars. Hubble's vision is so sharp it can
even measure the motion of many of these stars, and
over a relatively short span of time.

Analyzing archived images taken over a four-year period
by Hubble's Advanced Camera for Surveys,
astronomers have made the most accurate measurements
yet of the motions of more than 100,000 cluster
inhabitants, the largest survey to date to study the
movement of stars in any cluster. A precise measurement
of star motions in giant clusters can yield insights
into how stellar groupings formed in the early
universe, and whether an "intermediate mass" black
hole, one roughly 10,000 times as massive as our Sun,
might be lurking among the stars.